This invention relates to an input device for key telephone sets, and more particularly to a type of input device by which alphabetical letters and numerals can be alternatively keyed in through an improved input means for dialing purpose.
One kind of conventional keyboard for key telephone sets is as shown in FIG. 1, wherein 10 numeral keys and 2 function keys are arranged in 3.times.4 keyboard.
Another kind of conventional keyboard for key telephone sets is as shown in FIG. 2, wherein English letters are incoporated into the numeral keys, such as that normally used in most northern American countries.
Telephone calls are usually made using telephone numbers which are generally formed in a group of designated digits. Therefore, numerals are the main input data and have been considered standard form for key telephone sets. As to how English alphabetical letters are also used as input so as to promote the function of the key telephone sets, no significant improvement has ever been made in the field. Two examples with English alphanumeric input are known as follows:
(1) The U.S. A T & T Corporation has made known a Genesis multi-functional telephone set for which a separate keyboard having a set of English alphabet keys provided beside the ordinary push-button keys, as shown in FIG. 3, so as to assist the user in matching an English name of the called party with the telephone number and making a phone call using a personal name.
(2) Another example is as shown in FIG. 4 wherein a LEFT key (L), a MEDIUM key (M), a RIGHT key (R), etc. are provided along with an ordinary keyboard used in the key telephone system adopted in northern American countries. Operations of this example, which may be called a "position selective input method for English letters," are as follows: ##STR1##
In the first example, since a separate keyboard for English letters is required to work together with the original push-button keys, a large keyboard has to be provide in the key telephone system, making the telephone set bulky and also expensive.
Although the second example is more economical in structure than the first one, it is inconvenient for the user to perform the complicated keying operations because each letter is entered by operating two different keys; therefore, the user has to shift his finger frequently over the keyboard when making a telephone call.